Abstract: To make full use of the advantages of flywheel energy storage for assisting frequency regulation of the power grid and considering operation economic factors, this paper studies the coordinated control strategy and optimal capacity configuration for flywheel energy storage to assist the thermal power units in participating in the primary frequency regulation of the power grid.Firstly, according to the frequency characteristics of the power grid and the frequency regulation characteristics of units, a coordinated control strategy of thermal power unit and flywheel energy storage is proposed to reduce the unit wear, suppress the reverse frequency regulation, and continuously manage the energy storage power. Then, the frequency regulation income is calculated based on the contribution index of integral power assessment for primary frequency regulation, and the capacity configuration for flywheel energy storage is optimized. Finally, according to the actual operation data of a power plant, the frequency regulation effect of the coordinated control strategy, the contribution index qualified rate of integrated power assessment and life cycle income with optimal capacity configuration are simulated and analyzed. The results show that the proposed method can effectively improve the frequency regulation performance of the unit and has a good operation economy.